This invention is generally directed to toner and developer compositions, and more specifically, the present invention is directed to toner compositions, including magnetic toner compositions, containing therein certain charge enhancing additives, which impart a positive charge to the toner resin particles. Developer compositions containing the phosphonium charge enhancing additives of the present invention are useful for causing the development of electrostatic latent images, including color images. Additionally the positively charged toner compositions containing the phosphonium additives of the present invention are particularly useful in electrostatographic imaging systems having incorporated therein a Viton coated fuser roll, since many of these additives do not react substantially with Viton, causing undesirable decomposition thereof, thereby adversely affecting image quality.
Developer compositions with charge enhancing additives, especially additives which impart a positive charge to the toner resin particles are well-known, reference for example U.S. Pat. Nos. 3,893,935, 3,944,493, 4,007,293, 4,079,014 and 4,394,430. Thus for example there is described, in U.S. Pat. No. 3,893,935 the use of certain quaternary ammonium salt as charge control agents for electrostatic toner compositions. In accordance with the disclosure of this patent, certain quaternary ammonium salts when incorporated into a toner material provided a composition which exhibited relatively high uniform stable net toner charge when mixed with a suitable carrier vehicle; and this toner also exhibited a minimum amount of toner throw off. Further there is disclosed in U.S. Pat. No. 4,338,390 developer and toner compositions having incorporated therein as charge enhancing additives organic sulfate and sulfonate compositions. A similar disclosure is contained in U.S. Pat. No. 4,394,430.
There is also described in U.S. Pat. No. 2,986,521, reversal developer compositions comprised of toner resin particles coated with finely divided colloidal silica. According to the disclosure of this patent the development of electrostatic latent images on negatively charged surfaces is accomplished by applying a developer composition having a positively charged triboelectric relationship with respect to the colloidal silica. Moreover there is disclosed in U.S. Pat. No. 4,298,672 positively charged toner compositions containing resin particles, and pigment particles, and as a charge enhancing additive alkyl pyridinium compounds and their hydrates of the formula as detailed in Column 3, beginning at line 14. Examples of alkyl pyridinium compounds disclosed include cetyl pyridinium chloride. While the developer compositions disclosed in the 672 patent are sufficient for their intended purposes it appears that the alkyl pyridinium compounds involved react with the polymer contained on Viton fuser rolls causing decomposition thereof. Also several of the other charge control agents disclosed in the prior art interact with certain fuser rolls, such as Viton fuser rolls, used in electrostatographic systems. This interaction causes the fuser to be adversely affected, resulting in deterioration of the image quality. For example, Viton fuser rolls may discolor and turn black, develop multiple surface cracks and harden, when certain charge control additive compounds are contained in the toner mixture.
One Viton fuser roll selected for use in electrostatographic copying machines, is comprised of a soft roll fabricated from lead oxide, and duPont Viton E-430 resin, a vinylidene fluoride hexafluoropropylene copolymer. This roll contains approximately 15 parts of lead oxide, and 100 parts of Viton E-430, which mixture is blended and cured on the roll substrate at elevated temperatures. Apparently the function of the lead oxide is to generate unsaturation by dehydrofluorination for crosslinking, and to provide release mechanisms for the toner composition. Excellent image quality has been obtained with Viton fuser rolls, however, in some instances there results a toner fuser compatibility problem when charge control agents are part of the toner mixture. For example, it appears that certain specific charge control additives, such as quaternary ammonium compounds, and alkyl pyridinium compounds, including cetyl pyridinium chloride, react with the Viton of these rolls. Thus cetyl pyridinium chloride when part of the toner mixture appears to be catalytically decomposed by the lead oxide contained in the fuser roll, resulting in a highly unsaturated compound, which polymerizes and condenses with the unsaturated Viton E-430 material. In view of this, the Viton fuser roll turns black, develops multiple surface cracks, and the surface thereof hardens, thereby causing deterioration in image quality.
Toner compositions having incorporated therein many of the above described charge enhancing additives are useful for causing the development of images formed on layered photoresponsive imaging devices comprised of a photogenerating layer in contact with a transport layer. These devices usually are charged negatively, rather than positively as is the situation with selenium photoreceptors, thereby requiring a toner composition that is positively charged in order that the toner particles may be suitably attracted to the electrostatic latent image contained on the photoreceptor surface. In view of this efforts have been devoted to obtaining developer compositions containing toner resins which are positively charged. Thus while many charge control additives are known, there continues to be a need for new additives. Specifically there continues to be a need for additives which will not interact with Viton type fuser rolls. Additionally, there continues to be a need for charge control additives which are thermally stable at high temperatures. Moreover, there continues to be a need for positively charged toner and developer compositions which are humidity insensitive since it is known that moisture contained in the atmosphere, or moisture from other sources, can adversely effect the electrical properties of the toner compositions involved.
Also the prior art charge enhancing additives are based on nitrogen containing compounds, while in contrast the charge enhancing additives of the present invention are derivable from phosphorus containing compounds, and therefore represent a new class of additives. These additives can be economically prepared in addition to the other favorable physical chemical characteristics possessed thereby as indicated herein. Also the additives of the present invention are substantial nontoxic, and they can be easily and permanently dispersed in toner resin particles. Moreover toner and developer compositions containing the phosphonium additives of the present invention provide compositions having desirable admix charging.